Due to rapid innovation in the electronic communication technology, a mobile phone becomes an inevitable instrument in our daily life. Without it, he or she feels loss in touch with his friends and relatives. In order to achieve high reliability in the transmitting and receiving signals, the quality and functionality of the antenna assembly play a major role in the mobile phone. There are generally two types of antenna assembly used in the mobile phone, i.e. built-in antenna assembly (which is generally contained within the casing of the mobile phone) or an exposed type (i.e. the antenna assembly projects outwardly from the casing of the mobile phone). A mobile phone with a built-in antenna assembly is preferred to when compared to ones having an exposed antenna assembly, since the latter may accidentally collides with an object, thereby rendering the ruin of the mobile phone. In addition, the built-in antenna assembly provides more attractive appearance. For aesthetic and portability reasons, the mobile phone is generally constructed in compact size. It is therefore the prime object of the manufacture to improve the functionality of the quality of the antenna assembly in the mobile phone.
When a monopole antenna is used as the built-in antenna assembly in the foldable mobile phone, the antenna assembly provides fine transmitting ability. However, a clear area of the mobile phone may affect the transmitting ability by of the antenna assembly (i.e. The clear area is located under the antenna assembly of the mobile phone without any metal material). When the mobile is in the folded position, the clear area changes, thereby deviating the resonance frequency and causing degradation of the signal transmission bandwidth. Under this condition, the vertical direction of the transmission characteristic of the antenna assembly gets worse.
Referring to FIG. 1A, an unfolded position of a conventional mobile phone 10 is shown to include a lower printed circuit board 14, an upper printed circuit board 16 and an antenna unit 12. The antenna unit 12 is mounted on the lower printed circuit board 14, and includes an insulated plate 122 and a radiating metal strip 120 that is responsible for providing the resonance frequency of the antenna unit 12. A flexible printed cable 18 interconnects and transmits signals between the lower and upper printed circuit boards 14, 16.
FIG. 1B is a perspective view of the conventional mobile phone 10 in a folded position (shown in upside down configuration for illustration), wherein the lower printed circuit board 14 is disposed above the upper printed circuit board 16. Under this condition, the volume of the vacuum chamber is altered by virtue of shielding of the upper printed circuit board 16, thereby deviating the resonance frequency and causing remarkable degradation of the signal transmission bandwidth.